The present invention relates to a process for the preparation of hydroxybenzaldehydes by oxidation of the corresponding hydroxybenzyl alcohols. More particularly, this invention relates to the preparation of salicylaldehyde from ortho-hydroxybenzyl alcohol (commonly called saligenol).
Various means for carrying out this oxidation have been proposed. Among those, there may especially be mentioned the oxidation of hydroxybenzyl alcohol by means of air or pure oxygen in the presence of a catalyst based on a noble metal such as platinum or palladium. The oxidation is generally carried out in the liquid phase at a low temperature in an aqueous, preferably alkaline, medium. Thus, in the case of ortho-hydroxybenzyl alcohol, the oxidation in an aqueous alkaline medium containing about 1% by weight of noble metal relative to the alcohol to be oxidized gives salicylaldehyde with yields which are between 70 and 80%, relative to the alcohol employed. However, it is found that this method needs extended reaction times, of the order of one to several hours, to give a high degree of conversion of the alcohol. Hence, the use of the method entails a reduction in the productivity of the apparatus. It was thus desirable to have available an oxidation process which makes it possible to overcome this disadvantage while retaining good selectivity of the oxidation reaction in respect of producing aldehyde.
We have now discovered a process which satisfactorily meets this objective.
It is, accordingly, an object of the present invention to provide a novel process for producing hydroxybenzaldehydes which overcomes the disadvantages of the prior art processes.
It is also an object of the present invention to provide a process for the production of hydroxybenzaldehydes which retains good selectivity in its production of the benzaldehydes and yet permits highly efficient use of the production apparatus.
Other objects of the invention will be apparent to those skilled in the art from the present disclosure.